Different amount of frames - Matinee

I notice strange things happens when I render some more complex(?) scenes. I am rendering a scene with lets say 2.000 frames through Matinee. Everything is fine but (I thing thats due to the complexity) some scene arent rendered with the same amount of frames. It should give me 2.000 frames but I have different results. Sometime it is 1997,1995 etc. So it is not perfect. It isnt to much problem that it is not exactly as Matinee says but every render is different and I need to have the same amount every time because I am making a 3D scene and having 1 frames of a diffrenece is not acceptable. So after hitting the render butto n-time I should have always have the same results.
The animation is usually good to some point. For example for first 500 frames the cameras are identical, after X frames I can see differences , there are missing few frames. I guess that is the problem.